1. Field of the Invention
The present invention relates to an optical disc controller for use in an optical disc apparatus which records information in, and/or reproduces information from, an optical disc using a semiconductor laser (red-color laser, blue-color laser, etc.) as a light source. More specifically, the present invention relates to an optical disc controller which determines the type of an optical disc mounted on an apparatus capable of recording information in, and/or reproducing information from, a plurality of types of optical discs having different physical structures and different logical structures, and which performs memory allocation (mapping) according to the determined type of the optical disc. The present invention also relates to an optical disc apparatus using such an optical disc controller.
2. Description of the Related Art
In recent years, studies and developments of digital versatile disc (DVD) technology, where compressed, digitalized image information can be recorded on a track of an optical disc as well as sound information, have been actively carried out. Examples of optical discs used for such DVD technology include, for example, DVD-ROM, DVD-R, DVD-RAM, or the like. These DVDs have different physical structures and different logical structures.
In an optical disc apparatus for recording information in and/or reproducing information from an optical disc, a signal recording surface of the rotating optical disc is irradiated with light from an optical pickup, such as a laser beam or the like. The light reflected by the signal recording surface of the optical disc is then detected by a light-receiving element of the optical pickup, in order to read a signal recorded in the optical disc, thereby generating reproduction information, such as image data or the like.
Conventional optical discs used for CD technology (CD-ROM, CD-R, CD-RW, etc.) have different logical structures but identical physical structures. Thus, recording or reproduction of information on a plurality of types of optical discs can be achieved by a common optical disc controller. However, optical discs used for DVD technology (DVD-ROM, DVD-R, DVD-RAM, etc.) have different physical structures and different logical structures. Therefore, for the purpose of recording/reproducing information on a plurality of types of optical discs using the same optical disc apparatus, it is necessary to incorporate different optical disc controllers exclusively used for respective physical structure types (CDs and DVDs), and process the different types of optical discs using different programs (firmware or μ-code) so as to compensate for differences in the logical structure among the optical discs.
In an information recording or reproducing process, a central processing unit (CPU), which conducts communications with a host computer, controls the optical disk controller to perform a focusing control operation, a tracking control operation, a seeking operation of moving an optical pickup to an intended position for recording or reproduction of information, or the like, according to requests from the host computer. In a conventional optical disk apparatus, separate optical disc controllers are provided for different types of optical discs having different physical and logical structures which can be used with the optical disk apparatus. Thus, it is necessary to rewrite a program for the CPU or replace the CPU with another new one according to the types of optical disc controllers and modifications to the specification (version upgrade or the like) of each type of disc. Therefore, in a conventional optical disc apparatus, it is necessary to provide an exclusive optical disc controller and resources, which are associated with a CPU corresponding to the optical disc controller, in accordance with the type of an optical disc which can be used in the optical disc apparatus.
However, in the case where reproduction compatibility or recording compatibility is established in a single optical disc apparatus for different types of optical discs based on DVD technology (DVD-ROM, DVD-R, DVD-RAM, etc.) in addition to optical discs based on conventional CD technology (CD-ROM, CD-R, CD-RW, etc.), even though optical discs usable in such an apparatus are limited to optical discs having a diameter of 12 cm, the amount of software for the CPU and the man-hour for development would increase, and more resources would be demanded for the same CPU and the same optical disc controller. Thus, such compatibility cannot be practically established based on a limited amount of resources. Adding more resources in order to establish such compatibility for different types of optical discs accordingly increases the production cost of the optical disc apparatus.
In an optical disc apparatus where a CPU controls an entire system thereof, in order to establish reproduction compatibility or recording compatibility, it is necessary to develop software for the CPU in accordance with the type of optical discs used. In such a case, a processing system for an optical device, which is standardized and marketed after production of the optical disc apparatus, is additionally installed in the optical disc apparatus. Thus, a processing system of the optical disc apparatus becomes complicated, and accordingly, the probability that a bug occurs in such a system is increased. Furthermore, even if an entire system structure of such an optical disc apparatus is reconsidered and reconstructed, the man-hour required for developing the software generally increases. Thus, the probability that a bug occurs in such a system is still high.
Thus, in the case where the number of types of optical discs supported by a single optical disc apparatus is increased, recording or reproduction processing for a conventionally-supported optical disc is adversely influenced, as well as that for a new type of optical disc, and as a result, the reliability of the optical disc apparatus decreases in many cases.